The flywheel in any motor driven unit is basically used to maintain standard angular velocity.
It is a very significant part of the mower and hence while repairing it you need to take a lot of care.
Here are Instructions for lawn mower repairs - how to remove flywheel from lawnmower.
The flywheel is usually encased quite well inside the mower. So to remove the flywheel, you need to clear some obstructions first.
The first thing to dismantle is the blower cover. Depending on the design you would have four simple screws that hold this cover in place. Some mowers would have head bolts too, if your mower has it them remember to use a torque wrench to tighten the head blots after the flywheel replacement. Some mowers may have the flywheel placed behind the fuel tank, so you also need to remove the fuel tank too.
Once you have removed these parts you should see the flywheel fastened with a large nuts to the crankshaft. These nuts are generally firmly secured to the flywheel so you may have to brace the flywheel so that you get the necessary force to unscrew the nuts and release the flywheel. When you are bracing remember that it involves a lot of force so brace it against something that can withstand that force and not snap under pressure. While removing the nuts, make a note of how they were placed earlier so that reassembling it is easier.
Once you have taken the nuts out, you must look at the keyway. These must be aligned between the flywheel and the crankshaft. If the crankshaft and flywheel have same sized slots, then you will have a rectangular or D shaped metal locking the two. If the two have slightly different sized slots, then you will have an L shaped pin.
Instructions For Lawn Mower Repairs Video - How to remove flywheel and blade on lawn mowers
First try to hold the flywheel and rotate just the blades and vice versa. If either of them move independently, then one of the keys or both of them are broken and require replacement. If the flywheel key is broken the wheel will come out easily without much effort. However, if that is not the case, you will need to use special equipment called pullers to detach the flywheel from the crankshaft.
These flywheel pullers are designed specifically for various models. The easiest way is to get these pullers from the company itself. These would be original and will fit the flywheel slots perfectly too. While you could do the job without the puller, using it will save you a lot of time, effort and strain. Besides, you also avoid the possibility of potential damage to the crankshaft which can be quite expensive mistake too.
The way the puller works is that you need to insert the nuts to the puller into the flywheel. Based on the design, the holes in the plate of the puller and the flywheel will align. Before fixing the plate, loosen the flywheel nut slightly. Now place the plate on top of the flywheel and tighten the nuts one by one. As you continue to tighten them, the flywheel will pop out.
The use of customised pulley can seem very expensive for a simple task and many people will try to use ordinary clutch or gear. While this seems a more economical option, the damage this can do is quite grave. If you make a mistake during the process, the damage could be permanent and you may not be able to use the engine again.